Cement retainer and bridge plug



March 16,1954 P. A, MCKENNA 2,672,199

K CEMENT RETAINER AND BRIDGE PLUG Filed March 12, 1948 Patented Mar. 16,1954 PATENT oFFicE 2,672,199 itf'r'AIN/ER AND Buinen 'PLUG atrick' A.McKenna, Washington, D. c. Application Maren 12, 1948, 'serial No.14,413

(o1. lesa-13) Claims;

This invention relates to cement retainers and bridge plugs used,primarily in .Oil andere .Walls to block oi or cement selected ystratatemporarily and in some instances permanently.

An object of the invention is toufacilitatel the operation of packingoir the selected strata at depths where the pressure may be exceedinglyhigh. In the drilling operations, being carried on today depths of fromtwo to three miles are not uncommon.A Such depths are frequentlynecessary in exploratory work before any sign of oilbearing strata isdeveloped and the pressure in the well at such depths iswconsiderable.My improved arrangement vinsures that an eiective seal may bemaintainedu under the` pressures l'developed at these depths.:` andconsequently permits an effective cernenting or bridging job.

Another object of the inventions tosimplify the construction of acjernent paclrer .without in any way detracting from the effectivenessof its operation in performingv its i-intended,function, therebyreducing the `cost qimproduction which is a considerable factorinasmuchas vsuch retainers may be used onlywonce,y and anum'ber of them may benecessary `during the completion of al single well..

Still a further object `Qf Vtheinvention istofso construct and arrangethe` vconstituer,1t elements or the mechanismthat therecisnopossibilityI of jamming any of the parts whiletheureta-inervis beinglowered and set in thewell. 4T-e, this end I provide aA tubular sleevesurrounding theentire retainer during the operation oi lowering -it intothe well, thereby4 precluding anyy possibility of the slips whichYultimatelytgrip the wall of the well casing expanding beforethe desiredlevel is reached and interferingV with the lowering operation. Not onlydoes the sleeve or tube perform the important function ,.justmentioned,but it is so arranged in conjunction with the elements of the retaineror vpacker per se aslto bring about an importantcooperative'function inobtaining the exceptionally eiec'tiye seal which constitutes one of theprimary objects of the invention. Y y, w

In the drawings, whereiriliken'lim"'e'ralsl refer to like partsthroughout the iigures;

Fig. 1 is ak longitudinal `sectional view of my improved'retainer; t Y ln l Fig. 2 is a smil-ar viewafter the packing elements and slips have,been set; A

Fig. 3 is a section throught-:3 9i Fig. 1; Y Fig. 4 illustrates the formassu l"edwby the cups when restrained` byntheenelosing boot- Fig. 5musuates traforo-assume. byjthsup when the restrain-t of the boot isreleased, and

` Fig. 6 illustrates the principle to which in large measure theeffective seal may be attributed.

Referring now to Fig. 1, the numeral I indicates a well casing intowhich the retainer assembly is lowered until it reaches the desireddepth.` The retainer assembly comprises a tubular mandrel I2lIexteriorly threaded with a coarse left-hand thread at its upper end, asindicated at It. The threaded upper end is adapted for securernent tothe lower end or" a string of pipe with which the retainer assembly islowered down the casing to the desired level. The lower end of themandrel l2 is belled outwardly as' indicated at l@ and a seat Il isprovided at the base of the enlarged portion for a buoyant ball iiiwhich is prevented from falling through the lower end of the tube by anapertured closure tu which is threaded into the lower end of the mandrelto form a cage within which the ball is free to iioat.

A lower expanding cone 22 is threaded over a shouldered portion 2Q ofthe mandrel and the threaded portion terminates at a cone shoulder 26which engages Ia second Shoulder on the mandrel lying substantially inthe transverse plane of the ball seat l1. The wall of the mandrel l2 atits lower end is flared to formi a shoulder 2t extending downwardly andoutwardly from the lower end of the mandrel.

About this ange 28 a resilient molded sealing cup 30 is seated so`thatthe portion of the cup on the inside of iiange 28 seats against thelower edge of the wall 32 which constitutes the lower extremity of themandrel and forms the side wall of the cage within which the balliioats. The cup includes a cylindrical neck portion 38 which lies abovethe fiange 28 and circumferentially engages wall 32 throughout itslength. The upper end of neck 38 seats against shoulder 2t of expandingcone 22 andk lies between the wall 32 of the cage and aperipheral langeSt depending from the lower ymargin of the expanding cone 22,A andproviding an annular pocket for the upper or free end of the neck.

A metallic ring 36 encircles and holds the neck 38 of the sealing cupunder substantial compression against the outside of cage wall 32, thering 36 being of the same outside diameter as that of flange 34 ofcone22 at its lower extremity and abutting against the under face of ilange34.

An upper expanding cone 40 isthreadedly engaged with the lower end of asleeve` member 42 which` is slidable along the lmandrel wall. A secondresilient molded sealing cup 4G is seated about a flared flange i8r ofsleeve yL32, which cor responds to ange 28 and is assembled to sleeve 42in the manner described in conjunction with lower sealing cup 3i). Anannular gasket 5t provides a seal between the sealing cup ll@ and thewall of mandrel l2. The upper sealing cup 46 is held in position againstsleeve t2 by ring 52 in the manner described with reference to the lowersealing cup.

Segmental slips 54 having lower gripping surfaces 55 and upper grippingsurfaces 5t are provided with inclined camming faces St which are heldin engagement with the inclined faces E2 of the expanding cones by meansof an elastic ring 64 encircling the central portion of the slipsegments. The lower gripping surfaces 5t are held in positive engagementwith expanding cone 22 by means of shear pins 6G.

I-Iere an important phase of the invention should be pointed out. Thesealing cups 3@ and 46 are preferably made of synthetic rubber andmolded. The cup material may be bonded or unbonded to the metallicsupporting flanges 28 and 48, but it has been found that unbondedneoprene rubber gives eminently satisfactory results.

Exclusive of the neck 33 previously described, each cup 30 comprises abase 'i8 just outwardly of the neck 38 and a lip 'i9 outwardly of thebase I8 and merging therewith on a transverse plane 80. As is apparent,each base 'i8 is thicker than its associated lip I9. In the formillustrated, the inner periphery of each base 'is tapers outwardlyrelatively sharply as compared with the taper of the inner surface ofeach lip i9, whereby the plane at is deilned by the merger of the innersurfaces of the lip and base of each cup. Obviously, the merger of thelip and base of each cup can be otherwise defined within the scope ofthe invention as claimed.

As illustrated graphically in Fig. 6, the outside diameter of each ofthe cups Sil from the free edge of its lip i9 inwardly to a point on itsbase 78 deilned by the transverse plane A-A of Figure 6 which is locatedYsubstantially in the plane of the outer edge of a flange 28 or i3 is aconstant diameter which, when unrestrained, as in Figure 6, issubstantially greater than the inside diameter of the casing it.However, as best seen in Figure l, when the cups 30 are stretched andcompressed for insertion into the boot 6.2, each isV elongated so thatthe inner terminus of the area of constant diameter extends yfrom thefree edge of each lip 'it to a point on the base 18 defined by thetransverse plane B-B, Figure l, which is located between the outer edgeof one of the rings 36 or 52 and the root of one of the ilanges 28 or 48but somewhat nearer the associated ring. Likewise, as seen in Figure 2,the inner terminus of the area of constant diameter moves axiallyoutwardly a short distance to the plane of the line C-C, Figure 2, whenthe boot 68 is removed and the cups expand into engagement with thecasing Ii). The line or plane C--C is located on the Ybase 'I8substantially midway between the outer edge of a ring 36 or 52 and theroot of the adjacent flange 23 or 48. Moreover, it is important to notethat the major portion of the work in obtaining and maintaining theimproved seal is carried on not by the lips 'F9 of the cups but by thebases 'I8 thereof. The thickness of the resilient cup material in thiscircumferential area is greater than the thickness requisite for whatmay be termed the outer free ends or lips of the cups which lie beyondsaid area. In the form illustrated the cups are tapered radiallyoutwardly on the inside from the plane of the shoulders 28 and 48. Theouter free ends serve to preclude any possibility ofthe cup wallsfolding back or buckling under severe pressures.

It is also important that the resiliency characteristic of the materialof which the sealing cups are formed be such that it may be stressedwithout loss of resiliency to an extent where its outside diameter isless than the inside diameter of the casing. An example may be given,but not by way of limitation, to illustrate the oversize diameter of thesealing cup material, when unrestrained. In a casing having an insidediameter of 4.892 inches the outside diameter of the cups from theregion of the flanges 23 and 48 throughout their length, whenunrestrained, may be approximately 5.3125 inches and the material shouldbe compressible without loss of its resilient characteristics to anoutside diameter of approximately 4.4375 inches. Such an arrangement hasbeen found eminently successful.

A sleeve or boot 68 receives the entire retainer assembly as thusdescribed, the inside diameter of the boot 68 being such as to clear thegripping surfaces of the slips when the latter are in the inoperativeposition and compress the sealing cups 30 and 4S in the mannerheretofore explained. The outside diameter of the boot 58 is, as shown,substantially less than the inside diameter of the casing l0. The bootS8 is open at the top but closed at the bottom as indicated at ill. Inpositioning the retainer assembly in the boot, the resilient sealingcups, because of their form, substance and relative proportions asheretofore described in reference to the inside wall of the casing, arestretched during the relative sliding movement of the boot and the restof the assembly. This stretching or longitudinal tensioning isaccompanied by a substantial compression of the material. It isbelievedthat the effective seal provided by the cups, and particularlyby the circumferential areas adjacent the flanges 28, 48, is largelyattributable to the outward radial pressure set up by reaction of theresilient and elastic material when partially released from thecombination of tension and compression stresses which had been set up inthe material during the assembling of the boot and retainer assembly.

In operation the retainer assembly and boot are lowered into the casingat the end of string of pipe secured thereto at the upper threadedportion I4 to the desired position. During the lowering operation valvesor jars in the pipe string above the retainer are opened and the welliluid enters the retainer from above to equalize the pressure inside andoutside the boot, thereby preventing collapse. During the loweringoperation the ball i8 floats in its cage. Openings or ports 55 in thewall of the boot adjacent the slips serve to equalize the pressureinside the boot between the cups.

When the retainer reaches the desired level in the well, the pumps atground level are started and fluid under pressure passes down the pipestring to blow off the boot. The ball i8 cannot blow down with the bootbecause it is housed in a cage and after the boot has been displaced theball floats up to seat at the upper end of its cage as soon as the pumpsat ground level are cut oil. This prevents the well fluid from enteringthe retainer through the tubular mandrel l2.

When the boot is blown oil, the upper and lower sealing cups, releasedfrom restraint, expand radially outwardly at once to form a sealingcontact with the well easing. By virtue of thev manner in which thesealing cups are associated with the mandrel and the force with whichtheir outer walls grip the inside wall of the casing on release of thecompressive and tensile strain due to the boot, an exceptionally strongseal is provided.

The pumps having been shut off after the boot was blown and the sealingcups having set, the pipe string by which the retainer was lowered intothe well is pulled up slightly, during which operation the upper cup 46is held against any possible upward slipping movement by reason of thepressure of the well iiuid above it. During this pull-up the upper endsof the, slips move over the upper expanding cone to force the uppergripping surface out against the restraining pressure of the elasticring 64 to engage the wall of the casing, `Substantially simultaneouslywith this movement the shear pins 66 are broken and the upward movementof lower expanding cone 22 against the slips forces the lower grippingsurfaces 56 outwardly into engagement with the casing wall. Thisoperation is possible because of the fact that the tubular mandrel l2and the lower expanding cone 22 threaded thereto, with its associatedlower sealing cup, is free to slide upwardly with reference to theslips, upper cone and sealing cup assembly.

Subsequent downthrust of the pipe string by which the retainer waslowered assures the set of the upper gripping surfaces 58, the pull-uphaving been positively stopped when the lower gripping surfaces of theslips engaged the wall of the casing.

After the cementing operation a bridging ball i2 may be dropped down thepipe string to seat upon shoulder l@ adjacent the upper end of thetubular mandrel l2 to seal the retainer from above. The pipe string bywhich the retainer was lowered is then backed 01T the tubular mandrell2. All the metal parts of the assembly are of drillable material.

As aforesaid, the pressures the plug must withstand are tremendous,However, the structure of each of thecups 30 and 4B is such as towithstand much more pressure than can previously known cups. In thefirst place, as the cups each have a normal outside diameter throughoutsubstantially its entire length which is greater than the insidediameter oi the casing l0, each cup is always under compression and isnot fully expanded even after the boot 68 has been removed and each cupis engaged with casing I0. This fact enables each cup to resist burstingpressures better than can a cup whose normal diameter is less than thatof the casing throughout its length except for the region of the cuplip.

Then, too, the cups of the invention are strengthened in the dangerareas by being provided with walls of increased thickness in the regionsof the anges 28 and 4B. Also, the flanges 28 and 48 provide internalreinforcements for the cups in the areas where the cups are mostvulnerable to bursting pressures.

Finally, the rings 52 and 36 cooperate with the flanges is and 2B,respectively to prevent the cups 3Q and Al from being stripped from thebases 42 and 32 when the cups are stretched and compressed sufficientlyto permit the boot 68 to be applied to the plug. This is an importantfeature as considerable stress must be imposed on the cups at this timeand known bonds between the cup necks and the metal parts lof themandrel consistently failed until the coopresilient sealing cup flxedlyengaged with said mandrel, said. cup comprising a relatively thick vbaseand a relatively thinner lip. depending therefrom, said lip and at leastan adjacent portion of said base providing an elongated cylindrical cupwall having an unrestrained outside diameter throughout its length whichis greater than the inside diameter of the casing, a downwardlyremovable sleeve of lesser diameter than said casing surrounding saidcupand holding the same under compression to permit the insertion ofsaid sleeve and cup into said casing, said entire cup wall upon removalof said sleeve being adapted to expand by its own resiliency suicientlyto engage the casing throughout the entire length of said cup wall, andsaid cup expanding progressively from said base to said lip as saidsleeve is removed, whereby said base engages said casing at leastslightly before said lip.

2. In a cement retainer and bridge plug for sealing off the casing of awell at a desired depth, the combination with a central tubular run-inmandrel, of at least a lower downwardly directed resilient sealing cupxedly engaged with said mandrel adjacent the lower end thereof, said cupcomprising a relatively thick base and a relatively thinner lipdepending therefrom, said lip and at least an adjacent portion of saidbase providing an elongated cylindrical cup wall having an unrestrainedoutside diameter throughout its length which is greater than the insidediameter of said casing, removable means normally compressing said cupto a diameter less than the inside diameter of said casing to permit theinsertion of said cup and mandrel into said casing, said entire cup wallupon removal of said removable means expanding by its own resiliencyinto sealing engagement with said casing, and said removable means beingremovable so that said cup wall expands progressively from said base tosaid lip, whereby said base engages said casing at least'slightly beforesaid lip.

3. In a cement retainer and bridge plug for sealing ofi the casing of awell at a desired depth, the combination with a central tubular run-inmandrel having upper and lower ends, of upwardly and downwardly directedresilient cups iixedly engaged with said mandrel in the region of saidupper and lower ends respectively, each cup comprising a relativelythick inwardly disposed base and a relatively thinner lip extendingaxially outwardly therefrom, the lip and at least an adjacent portion ofthe base of each cup together providing an elongated cylindrical cupwall having an unrestrained outside diameter throughout its length whichis greater than the inside diameter of said casing, a downwardlyremovable sleeve of lesser diameter than said casing surrounding both ofsaid cups and holding the same under compression to permit the insertionof said mandrel and cups into said casing, said cup walls upon removalof said sleeve expanding by their own resiliency into sealing engagementwith said casing throughout the entire 7 lengths of said cup walls, andsaid downwardly directed cup expanding progressively from said base tosaid lip as said sleeve is removed, whereby its base engages said casingat least slightly before its lip.

4. In a cement retainer and bridge plug for sealing oil the casing of awell at a desired depth, the combination with a central tubular run-inmandrel, of deformable and resilient means surrounding said mandrel andxed thereto, said sealing means having an upper and lower end, saidsealing means having an elongated cylindrical outer surface engageablethroughout its length with said casing to seal the latter, said sealingmeans when unrestrained having an outside diameter throughout the lengthof said cylindrical outer surface which is substantially greater thanthe inside diameter of said casing, removable means compressing saidsealing means to an outside diameter less than the inside diameter ofsaid casing to permit the insertion of said mandrel and sealing meansinto said casing, and said removable means being so removable that saidsealing means expands progressively from said upper to said lower end,whereby said upper end engages said casing at least slightly before saidlower end.

5. The structure of claim 4, wherein said sealing means is fixed to saidmandrel adjacent the lower end thereof, a second and similar resilientand deformable sealing means surrounding said mandrel and xed theretoadjacent the upper end thereof, said second sealing means beingoperative in the same manner as said irst named sealing means, and saidremovable means comprising a single, downwardly removable sleevesurrounding both of said sealing means.

PATRICK A. MCKENNA.

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